This invention relates to machines for pasteurizing alimentary liquids and/or for making ice-cream or similar frozen congealed products, said machines being equipped with gas-compression refrigerators.
More particularly, the invention relates to a method of pasteurizing said liquids or ice-cream products within said machines, and of sterilizing the elements of the machine contacting said liquids and ice-cream products.
One of the most hard problems in the field of ice-cream making machines of non-industrial type, namely those machines for a relatively limited daily production (such as the machines for the production and distribution of "express" ice-creams to consumers, the pasteurizing machines and the like), is the problem of sterilizing all the elements of the machine contacting the ice-cream and/or ice-cream mixture, such as the mixture feeding tank and conduits and the members associated therewith, the freezing cylinder and conduits and members associated therewith, the emulsifying and mixing pumps, and the like.
Another problem related to these machines and to this type of production is the pasteurization and preservation in sterilized conditions of the mixture, either liquid or turned into ice-cream, remaining in the machine in the periods of rest or preservation, for example from the evening of one day to the morning of the day after.
These problems can be solved partially by washing the machine every day; however, this washing does not assure always the desired results, due to the difficulty to reach some elements of the machine (such as conduits, pumps, etc.) and because said washing entails the loss of the product left in the machine.
It has been proposed, for example, as described in the Italian Patent No. 736656, to effect said sterilization by arranging, in the freezing cylinder and in the mixture feeding tank, suitable electrical heating resistances to heat the contents of said elements to bacteria-killing temperatures.
However, the arrangement of electrical resistances contacting directly the feeding tank and the freezing cylinder gives rise to problems the technical solution of which is not easy.
The object of this invention, therefore, is to overcome the drawbacks of the conventional ice-cream making machines by providing a system permitting, in a simple and economic way and with no substantial modification of the machine, to heat the liquid mixture and the ice cream and all the parts of the machine contacting the ice-cream and/or the liquid mixture to bacteria-killing temperatures.
Under one aspect, this invention relates to a method of pasteurizing ice-cream and mixtures for ice-cream and of sterilizing the elements of the ice-cream making machines (or of pasteurizers) contacting said mixtures and ice-cream, which is applicable to the machines that are provided with gas-compression refrigerating units, comprising the steps of conveying the hot compressed gas coming from the compressor through the evaporator (or evaporators) of the refrigeration circuit arranged in heat-exchange relationship with the elements of the machine to be sterilized, by-passing the condenser and expansion valve (or valves) of said refrigeration circuit; of permitting this compressed gas to flow through said evaporator to reach the desired sterilization temperatures in the machine; and of resuming the refrigeration cycle by re-inserting the condenser and expansion valve (or valves) in the circuit and by excluding the by-pass circuit.
Another object of this invention is to provide a machine for carrying said method into effect, characterized in that inserted between the delivery conduit of the compressor and the evaporator of the refrigerator (in heat exchange relationship with the elements of the machine to be subjected to heat) is a by-pass circuit for the condenser and expansion valve (or valves) of the refrigerating circuit, controlled by one or more switching valves.